intranasal oxytocin and a polymorphism in the oxytocin...
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Intranasal oxytocin and a polymorphism in the oxytocin receptor gene are associated with human-directed social behavior in golden retriever dogs Mia Persson, Agaia J. Trottier, Johan Bélteky, Lina Roth and Per Jensen
The self-archived postprint version of this journal article is available at Linköping University Institutional Repository (DiVA): http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-142438 N.B.: When citing this work, cite the original publication. Persson, M., Trottier, A. J., Bélteky, J., Roth, L., Jensen, P., (2017), Intranasal oxytocin and a polymorphism in the oxytocin receptor gene are associated with human-directed social behavior in golden retriever dogs, Hormones and Behavior, 95, 85-93. https://doi.org/10.1016/j.yhbeh.2017.07.016
Original publication available at: https://doi.org/10.1016/j.yhbeh.2017.07.016
Copyright: Elsevier http://www.elsevier.com/
Intranasal oxytocin and a polymorphism in the oxytocin receptor gene are associated with human-directed social behavior in golden retriever dogs
Mia E. Persson, Agaia J. Trottier, Johan Bélteky, Lina S.V. Roth & Per Jensen*
IFM Biology, AVIAN Behaviour Genomics and Physiology Group, Linköping University, Linköping, Sweden * Corresponding author: P. Jensen, IFM Biology, AVIAN Behaviour Genomics and Physiology Group, Linköping University, 581 83, Linköping, Sweden. E-mail: [email protected]
Abstract
The oxytocin system may play an important role in dog domestication from the
wolf. Dogs have evolved unique human analogue social skills enabling them to
communicate and cooperate efficiently with people. Genomic differences in the
region surrounding the oxytocin receptor (OXTR) gene have previously been
associated with variation in dogs’ communicative skills. Here we have utilized
the unsolvable problem paradigm to investigate the effects of oxytocin and OXTR
polymorphisms on human-directed contact seeking behavior in 60 golden
retriever dogs. Human-oriented behavior was quantified employing a previously
defined unsolvable problem paradigm. Behaviors were tested twice in a repeated,
counterbalanced design, where dogs received a nasal dose of either oxytocin or
saline 45 min before each test occasion. Buccal DNA was analysed for genotype
on three previously identified SNP-markers associated with OXTR. The same
polymorphisms were also genotyped in 21 wolf blood samples to explore
potential genomic differences between the species. Results showed that oxytocin
treatment decreased physical contact seeking with the experimenter and one of
the three polymorphisms was associated with degree of physical contact seeking
with the owner. Dogs with the AA-genotype at this locus increased owner
physical contact seeking in response to oxytocin while the opposite effect was
found in GG-genotype individuals. Hence, intranasal oxytocin treatment, an OXTR
polymorphism and their interaction are associated with dogs’ human-directed
social skills, which can explain previously described breed differences in
oxytocin response. Genotypic variation at the studied locus was also found in
wolves indicating that it was present even at the start of dog domestication.
Keywords: Oxytocin, oxytocin receptor gene, OXTR, domestic dog, canine, wolf,
canis lupus, behavior genetics, canine behavior, social behavior
Introduction
Domestic dogs have apparently evolved unique human analogue communicative
skills during the course of domestication and through sharing our ecological
niche (Topal et al., 2009). This social competence involves comprehension of
referential gestures as well as ostensive cues such as pointing and gazing
(Lakatos et al., 2012; Soproni et al., 2001). Dogs are e.g. more skillful than both
their wolf ancestors and chimpanzees in understanding human communicative
behavioral cues during an object choice paradigm (Hare and Tomasello, 1999,
2005). Although primate species have previously been the main focus organisms
in comparative social cognition research trying to understand the origin of
humans’ social skills (Hare et al., 2012), dogs may therefore be equally
interesting models.
The differences between dogs and wolves are evident also when studying fully
socialised individuals. Wolves do not seek as much human contact as dogs (Gacsi
et al., 2009; Topal et al., 2005) and do not use mutual gazing as a mean of
communication (Nagasawa et al., 2015). Dogs are able to display intentional
referential communicative gestures towards humans, involving both an
attention-seeking component as well directional “showing” behaviors (Marshall-
Pescini et al., 2013; Miklosi et al., 2000; Passalacqua et al., 2011). When faced
with an unsolvable problem, dogs usually turn to a nearby human for help while
wolves do not show this behavior to the same extent (Miklosi et al., 2003). Hence,
the evidence suggests that this human-directed social behavior has largely been
shaped during domestication.
In spite of the much larger inter-species social competence of dogs, there is still
considerable within-breed variation in this trait (Persson et al., 2015). Recent
evidence shows that there is a significant genetic basis for this variation: In one
population of beagles, the narrow-sense heritability of human-directed social
behavior was estimated to 0.23 and candidate genes were identified through
genome-wide association analysis (Persson et al., 2015; Persson et al., 2016).
Based on its well-established function in social bonding in humans and other
mammals (Lim and Young, 2006), it has been suggested that the neuropeptide
oxytocin may also play a central role for the unique dog-human bond (Nagasawa
et al., 2015). Hence, genetic variations in the oxytocin system may play a role in
within- and between-breed differences in human-oriented social behavior and in
the bond with the owner (Beetz et al., 2012).
Oxytocin is produced in the hypothalamus as well as in the periphery and can
both act as a neurotransmitter and a neurohormone (Gimpl and Fahrenholz,
2001; Neumann, 2008). Peripheral oxytocin concentrations can increase in both
humans and dogs as a result of tactile interaction (Handlin et al., 2011; Mitsui et
al., 2011; Odendaal and Meintjes, 2003; Rehn et al., 2014) and mutual gazing
(Nagasawa et al., 2009; Nagasawa et al., 2015). However, it has been suggested
that it is mainly central and not peripheral oxytocin playing a role in influencing
behavior (Leng and Ludwig, 2016). Although the mechanisms are yet poorly
understood, peripheral and central (Neumann et al., 2013; Rault, 2016) oxytocin
concentrations can be experimentally manipulated though intranasal
administration (Leng and Ludwig, 2016), although the increase in central
oxytocin upon intranasal administration seems to be small (Rault, 2016).
In spite of this, intranasal administration of this hormone in dogs has been
shown to increase positive expectations (Kis et al., 2015), mutual gazing with the
owner (Nagasawa et al., 2015), affiliative behavior towards both their owners
and conspecifics (Romero et al., 2014), play behavior (Romero et al., 2015) and
performance in an object choice task relying on human given pointing cues
(Oliva et al., 2015). However, oxytocin does not always have pro-social effects
and there seems to be both individual variation and contextual components
determining the exact effects of oxytocin (Bartz et al., 2011). For instance, in
humans it may decrease trust and cooperation directed towards strangers or
members of an out-group (De Dreu, 2012; De Dreu et al., 2010; De Dreu et al.,
2011) and in dogs it may decrease friendliness in a threatening situation
(Hernadi et al., 2015). Additionally, breed differences have been described in the
effects of oxytocin administration (Kovacs et al., 2016a).
Several studies have also reported sex differences in dogs’ responses to oxytocin.
In females but not in males, intranasal oxytocin administration increased mutual
gazing with humans (Nagasawa et al., 2015), looking time in a social motion
perception test (Kovacs et al., 2016a) and performance with following human
ostensive cues (Oliva et al., 2015). Hence, it is important to take both breed and
sex into consideration when investigating effects of oxytocin in dogs.
The effects of oxytocin depend both on the hormone levels and the receptor
activity. Both oxytocin and the oxytocin receptor (OXTR) are highly conserved
and present in mammals as well as several other taxa (Gimpl and Fahrenholz,
2001). In humans, variation in the OXTR gene have e.g. been associated to autism
(Jacob et al., 2007), attachment style (Denes, 2015), temperament (Tost et al.,
2010), empathy and stress reactivity (Rodrigues et al., 2009). However, variants
of the OXTR gene have not yet been as widely studied in dogs.
Among the existing studies, Kis et al. (2014) tested Border Collies and German
Shepherds in a battery of social test situations and genotyped them at three
different single nucleotide polymorphisms (SNPs) surrounding the OXTR gene.
Associations were found between specific SNP genotypes on one hand, and
human proximity seeking and friendliness on the other. Interestingly, German
Shepherds carrying the A allele of the rs8679684 marker and the G allele of the
19131AG marker were more friendly while the opposite pattern was seen in
Border Collies. These results corroborate the importance of taking breed into
consideration when investigating oxytocin effects. Another study investigated
the effects of genetic variation around OXTR on object choice task performance
in pet and shelter dogs of different breeds (Oliva et al., 2016). Although 10
microsatellite markers surrounding the gene were studied, no significant
associations were found with task performance. Twelve wolves were also
included in the genetic analysis, revealing two genetic markers with significantly
different genotype ratios between species.
The contradictive effects of oxytocin on social behavior in both humans and dogs
suggest that we are still far from understanding its proper function and
mechanism. One possibility is that individuals with different genotypes
associated with the OXTR gene respond differently to oxytocin treatment. In
humans, OXTR genotypes have been shown to affect the behavioral responses to
intranasal oxytocin treatment (Feng et al., 2015; Marsh et al., 2012). To our
knowledge, the effects of oxytocin depending on genetic variants in the vicinity
of OXTR have not yet been examined in dogs.
The aim of the present study was to investigate the effects of intranasal oxytocin
treatment, genetic variation in association with OXTR and interactions between
hormone treatment and genotype on human-directed social behavior of dogs in
the unsolvable problem paradigm. Additionally, given the differences between
dogs and wolves in human communicative skills, we also aimed to examine
genotypic differences between the species at the same genetic markers
surrounding the OXTR gene.
Methods
Ethical note
This study protocol was performed in accordance with the ethical permit
approved by the regional ethical committee for animal experiments in Linköping,
Sweden (permit number: 51-13) with all owners giving their informed consent
for their dogs’ participation in this study. The methods were carried out in
accordance with the relevant guidelines.
Subjects
Sixty golden retriever dogs (34 females and 26 males) were tested and
genotyped to investigate the effects of intranasal oxytocin and OXTR genotype on
human-directed social behavior. Owners were recruited to participate in the
study through social media, local advertisement and radio. The dogs were
required to be registered by the Swedish Kennel Association as purebred golden
retrievers, not to be pregnant or lactating and at least 4 months old (mean age of
5.1 ± 0.47 years ± SE; range 4 months-12 years). Buccal samples were collected
from the golden retrievers for genotyping of three genetic markers (SNP)
associated with the OXTR gene. Additionally, 21 wolf samples (7 females and 14
males) were used for genotyping for the same genetic markers. Eighteen wolf
blood samples were supplied from Kolmården Wildlife Park, Sweden and three
wolf DNA samples previously isolated from brain tissue were originally supplied
from Borås Animal Park, Sweden. All wolves belong to the Scandinavian
population (Canis lupus lupus) and were either raised at the wildlife parks or
wild captives.
Procedure
DNA Sampling
Buccal samples were collected at the start of the first testing session of each
individual, by asking the owner to rub a cotton swab on the inside of their dogs´
cheek for approximately 20 seconds. Samples were genotyped for the same three
single nucleotide polymorphisms (SNPs) as previously described by Kis et al.
(2014) (Fig 1). Sequencing primers for pyrosequencing were designed using the
software PyroMark Assay Design 2.0.1.15 by QUIAGEN©. All primers were
manufactured by Thermo Fisher Scientific (Waltham, MA, USA) and the
sequences can be found in Table 1.
Table 1: Primer sequences.
Primer Sequence (5´-3´)
212AG Forward TACCCCCAACGGGGATTTC
212AG Reverse BIOTIN-GCCCCAGGAACCCCAAGT
212AG Sequencing TGAACAGCACCCCCG
rs8679684 Forward BIOTIN-TTCTCCTGGACCTATCATTTCACT
rs8679684 Reversed GCTTAGAACACTAGGCTTCCACAC
rs8679684 Sequencing GGGTGTTACCAATCCT
19131AG Forward GGGTGTGGAAGCCTAGTGTTCTAA
19131AG Reversed BIOTIN-CCATGCAAAAGTAAAAGCACTCTG
19131AG Sequencing TGGAGGGTGGTGCTA
Treatment
The same two female experimenters (first and second author, referred to in the
following as E1 and E2) carried out all the treatments and experiments. Upon
arrival at the testing location, each owner was thoroughly informed about the
procedure by E1. At the first visit of each individual dog the owner, under
supervision of E1, collected the buccal DNA sample. Subsequently, intranasal
treatment was administered by E1. All dogs were tested at two different
occasions (10 ± 4 days apart). At the first occasion, dogs received either oxytocin
or control (saline) treatment. The order of treatments was predetermined,
pseudo-randomized and counterbalanced between sexes so that half of the
subjects received oxytocin on the first occasion and the other half saline.
Treatments were blind to experimenters as well as owners.
Previous studies have administered 12 IU (Kis et al., 2015), 24 IU (Oliva et al.,
2015) and 40 IU (Romero et al., 2014) doses of oxytocin, all with significant
behavioral effects. Based on this, we decided to use 20 IU in order to be certain
to have a biologically potent dose. Intranasal treatments contained either 20 IU
oxytocin (O4375, Sigma) dissolved in 0.4 ml of phosphate-buffered saline
(saline) or 0.4 ml saline only. One half dose (0.2 ml) was administered to each
nostril via a Mucosal Atomization Device and a 1 ml syringe. Blinding of
treatments was achieved in the following way: E2 prepared the treatment
solutions each testing day but these were administered to the dogs by E1. Both
E2 and the owners were blind as to which treatment their dogs received at the
given occasion. E2 carried out the behavior recordings (see below) but was not
provided with the treatment information until after all the video analysis was
finished.
Behavior Test
Behavioral tests were carried out outside, at four different locations in Sweden
(Linköping University, SBK Gothenburg, a private kennel outside of Norrköping
and at another private kennel outside of Söderköping). The owners brought the
dogs to the test site in their own cars, and were told to arrive well before the
start of the testing to allow dogs to settle after the transport. Dogs were tested
inside a 3 x 3 m marquee tent with walls on three sides and without flooring and
placed on a short-cut grass lawn. To keep the dogs inside the testing area (the
tent) a mesh fence was placed at the open side. Behavioral tests were recorded
with an HD camcorder (Canon Legria HF G25) placed on a camera stand
approximately 3 m behind the tent opening.
After DNA sampling and treatment administration, and before the behavior test,
willingness to eat the treats used in the behavioral test was verified by
presenting three quarter pieces of Frolic® on a plastic plate of the same material
as used in the problem-solving device. A thorough description of the procedure
can be found in Persson et al. (2015). All subjects consumed the treats offered
within 20 seconds. After the feeding test, owners were asked to walk their dogs
for 30 minutes and then let them rest in the car for 10 minutes prior to testing to
allow 40-45 minutes to pass between treatment administration and behavioral
testing. They were instructed to not treat their dogs differently than usual during
the walk but to avoid contact with unknown dogs or humans. If the owner
brought more than one dog to the test, the dogs were sampled, treated and
tested approximately 5-7 minutes apart.
The problem device used for the behavior tests was the same as previously
described by Persson et al. (2015). It consisted of a plastic tray (548 x 248 mm)
with three symmetrically placed round wells (70 mm in diameter) covered by
transparent plexiglas lids with odour ports. Dog treats (Frolic®) were placed
underneath the three lids. In order to access the treats the dog has to push the lid
to the side, however one of the lids was tightly fastened and not possible to open.
When the dog and its owner arrived at the testing arena, the unsolvable problem
device had already been prepared and placed on the ground 15-30 cm from the
middle of the back wall inside the tent.
Owners had previously been instructed to stand immediately inside the fence in
the front right corner of the tent with the dog still on the leash. E2 was standing
on the opposite side of the tent in the front left corner. When the fence gate was
closed, E2 asked the owner to unleash the dog and as soon as the dog was off the
leash E2 started a stopwatch timer and the three minutes of continuous
recording started. The dog was allowed to freely move around inside the tent
during this time period, however if attempting to escape, the owner was allowed
to stop the dog from leaving the tent. Through the testing period, E2 was
standing passively facing the problem task and the owner had previously been
instructed to do the same. However, if the dog failed to solve any of the solvable
parts within 60 seconds, E2 opened both solvable lids halfway and immediately
walked back to her original position. The testing equipment was cleaned
between each subject.
Ethogram and data analysis
Behavioral analysis was performed from video recordings using The Observer
XT 10 software. When owners signed up to participate they supplied the
pedigree ID-number, sex and date of birth of the dog. Date and time of testing
were also noted. The ethogram used for the behavioral analysis is shown in
Table 2. For each behavior described in the ethogram the duration, frequency
and latency were recorded.
Table 2: Ethogram of behaviors used in the analysis.
Behavior Description
Experimenter zone Dogs’ head is within its own body length of the
experimenter
Owner zone Dogs’ head is within its own body length of the owner
Experimenter gaze The dog gaze towards the face of the experimenter
Owner gaze The dog gaze towards the face of the owner
Experimenter physical
contact
The dog is in physical contact with the experimenter
Owner physical contact The dog is in physical contact with the owner
DNA extraction and genotyping
Buccal swabs were stored at 4°C and blood/serum samples were stored at -20°C
until DNA extraction. From buccal swabs, DNA was extracted from buccal cells
using the standard protocol of the Isohelix kit DDK-50. However, the samples
were kept in Lysis Buffer and proteinase K for 48 hours prior to continuing with
the protocol. Single 50 μl elisions were used. Wolf samples consisted of 15 full
blood samples, three serum samples as well as three samples of previously
extracted DNA from brain tissue ready to use in the next step. DNA was extracted
from blood and serum samples using the standard protocol of the QIAGEN
DNeasy® Blood and Tissue Kit. DNA yield was subsequently quantified using a
Nanodrop ND-1000 and stored at -20°C until further use.
Real-time polymerase chain reaction (qPCR) with subsequent pyrosequencing
was used in order to genotype golden retrievers and wolves for each of the three
SNP markers. The reaction mixture for the qPCR contained 10 μl SYBR, 5 μM
each of forward and reverse primer, 2 μl DNA template and 6 μl water. The qPCR
was performed in a Lightcycler®480II Roche at a total volume of 20 μl per
sample. The program consisted of an initial denaturation at 95 °C for 10 min, a
touchdown protocol with four amplification cycles starting with an annealing
temperature of 63 °C, reduced by 1 °C/cycle to 60 °C. This was followed by 40
cycles of 15 s denaturation at 95 °C, 30 s annealing at 60 °C and 30 s extension at
72 °C. The DNA templates were then subjected to a melting step from 70 °C to
90 °C with a 0.1 °C step increase, each step was held for 2 s.
After DNA amplification, pyrosequencing was performed on the entire 20 μl
qPCR product volume according to the PyroMark Q24 Vacuum Workstation
Quick-Start Guide found at www.quiagen.com. Genotyping results were analysed
using the PyroMark Q24 2.0.6 software.
Statistical analysis
All statistical analysis, except for Hardy-Weinberg Estimates, was carried out
using IBM SPSS version 22.0 software. Behavioral data was checked for
normality with the Kolmogorov-Smirnov test as well as visually. When necessary
data was transformed (log10 (x +1)). Generalized Linear Mixed Models analysis
(GLMM) for repeated measures was used for the statistical analysis. Models
consisted of fixed effects of sex, treatment, genotype and the interaction between
treatment and genotype. Only the genotype of the 19131AG SNP was analysed as
all individuals were fixed for the same genotype at the two other loci. Dog ID was
set as a random factor and the data distribution was set to either normal with a
link function or gamma with a log function. Factors with the highest p-values
were removed from the model if it increased the model fit. Best model fit was
determined though comparison of Akaike measurements. Akaike measurements,
models and distributions are presented in the Appendix. Bonferroni was used to
account for multiple testing. Hardy-Weinberg Estimates (HWE) was calculated
using the exact test incorporated in the “genetics” package in R. Cohen’s d
estimates were calculated using t-values from post hoc pairwise comparisons in
a web-based effect-size calculator
(http://www.campbellcollaboration.org/escalc/html/EffectSizeCalculator-
Home.php).
Results
Genotyping was successful in all 60 golden retrievers and 21 wolves. All samples,
both from dogs and wolves, were fixed for the A-allele at the 212AG and
rs8679684 SNPs. However, individual variation was found in the 19131AG SNP
in both golden retrievers (HWE p = 0.38) and wolves (HWE p = 0.12). Genotype
frequencies are displayed in Figure 2. Final statistical models, means and p-
values for all behaviors can be found in the Appendix.
Intranasal oxytocin administration significantly decreased the frequency of
experimenter physical contact seeking (Fig 3a; F1,118 = 6.53, p < 0.01). No
significant effects of oxytocin administration were found for any of the behaviors
directed towards the owner.
Independent of treatment, the 19131AG genotype had a significant effect on the
latency to owner physical contact (F2,117 = 7.17, p < 0.01) where AA individuals
sought contact earlier than AG and GG dogs (Figure 4). There was no effect of the
marker genotype on social behavior towards the experimenter.
Treatment and genotype showed a significant interaction effect on the frequency
of owner physical contact (F2,113 = 5.21, p < 0.01) where dogs with AA genotype
increased contact frequency after oxytocin treatment while GG genotypes
showed the opposite reaction (Fig 5a). Treatment and genotype did not have an
overall significant effect on duration of owner physical contact. However, there
was a significant effect of treatment within individuals carrying the GG-genotype
(Figure 5b; Bonferroni adjusted p = 0.02, Cohen’s d = 0.61). There were no
significant interaction effects for behavior directed towards the experimenter.
Sex significantly affected duration (F1,118 = 5.13, p = 0.03) and frequency (F1,118 =
7.85, p < 0.01) of experimenter gaze, where females were seeking more eye
contact. Male dogs spent significantly more time than females in the owner zone
(F1,118 = 4.30, p = 0.04).
An effect of treatment order was found on the duration of experimenter physical
contact (F1,117 = 4.87, p = 0.03) where dogs receiving oxytocin treatment at the
first occasion had less physical contact across both trials. Testing occasion also
had effects on some human-directed behaviors. Regardless of treatment
(oxytocin or saline), at the second test occasion, dogs spent more time in the
experimenter zone (F1,117 = 9.91, p < 0.01), and were in the experimenter zone
more frequently (F1,117 = 6.29, p < 0.01) than at the first occasion. They also
showed longer duration of experimenter gazing (F1,117 = 19.10, p < 0.00), higher
frequency of the same (F1,117 = 24.70, p < 0.00), and increased frequency of
owner gazing during the second test occasion (F1,117 = 8.42, p < 0.00).
Discussion
This study investigated the effects of intranasal oxytocin administration and a
polymorphism associated with the oxytocin receptor gene, OXTR, on human-
directed social behavior in golden retriever dogs. We found that administration
of oxytocin had significant effects on contact seeking behavior and genotype was
found to be associated with some of this behavioral variation. There was also a
significant treatment x genotype interaction. Furthermore, we found a similar
polymorphism in wolves, indicating that the genetic variation related to OXTR
may have been present already in the ancestors of domestic dogs.
We genotyped three different SNPs closely associated with the OXTR gene and
previously found to be polymorphic in some dog breeds. Whereas both wolves
and golden retrievers had genotypic variation in one and the same of the three
studied SNPs (19131AG), they were all fixed for the A-allele at the 212AG and
rs8679684 locus that have been shown to vary in other breeds (Kis et al.,
2014)(see also preliminary data in the supplementary material of Kovacs et al.
(2016b)). This could indicate that the 212AG and rs8679684 polymorphisms
have appeared after the historical split between dogs and wolves. These SNPs
could therefore be associated to genomic changes affecting the OXTR gene
appearing during dog domestication, possibly even targeted by selection.
At the 19131AG locus, golden retrievers mostly carried the GG and AG
genotypes while wolves either had the AA or AG genotype. The fact that we
found genetic variation in both golden retrievers and wolves at the same locus
suggests that this polymorphism was already present among wolves prior to dog
domestication. Although none of the wolf samples carried the GG genotype, this
may be a result of small sample size of 21 individuals. The presence of AG
individuals shows that the G-allele is present within the wolf population but is
probably not as common as the A-allele. Similar to our results, Kis et al. (2014)
found that the G-allele was more common among Border Collies where it was
almost fixed within the Hungarian population. However, German Shepherds, like
the wolves in our studies, mostly carried the AA or AG genotype. It therefore
appears that OXTR-related polymorphisms vary between breeds, which may
possibly be linked to selection during domestication and modern breeding of
purebred populations, selected for different behavioral traits. This corroborates
suggestions by (Oliva et al., 2016), who found significant breed differences in
allele distribution of microsatellites surrounding the OXTR in different breeds
and wolves.
In the present study, oxytocin treatment alone affected how dogs were seeking
physical contact from a previously unknown experimenter. There is evidence of
oxytocin playing a significant role in the social bond between dogs and their
owners (Nagasawa et al., 2009; Nagasawa et al., 2015; Romero et al., 2014).
Although oxytocin is mostly known to enhance social behavior (Carter, 2014), in
this case, dogs in fact sought less contact with the experimenter upon oxytocin
administration. This is in agreement with previous research showing that
intranasal oxytocin treatment does not always have pro-social effects in either
humans (Bartz et al., 2011; De Dreu, 2012) or dogs (Hernadi et al., 2015). This
could be due to a contextual as well as an individual factor affecting the effects of
oxytocin (Bartz et al., 2011). There is also recent evidence of breed differences in
oxytocin response. Kovacs et al. (2016b) found that intranasal oxytocin
administration increased gazing towards an experimenter in Border Collies but
decreased the same behavior in Siberian Huskies. The authors suggest that
genetic differences between breeds may cause these differences.
Oxytocin is not believed to pass the blood-brain barrier in significant amounts
(Leng and Ludwig, 2016). There are studies showing that intranasal
administration of oxytocin can increase central oxytocin slightly (Leng and
Ludwig, 2016; Rault, 2016). However, there are also studies finding no increase
(Leng and Ludwig, 2016). In spite of this, several studies have measured
behavioral effects of peripheral oxytocin administration in dogs, although the
mechanisms are still unknown. E.g. exogenously administrated oxytocin has
been shown to increase dogs’ positive expectations (Kis et al., 2015), social play
behaviour (Romero et al., 2015), following of human ostensive cues (Oliva et al.,
2015), affiliative behaviors towards both humans and conspecifics (Romero et al.,
2014) and mutual gazing with the owner (Nagasawa et al., 2015). Additionally,
behaviors such as dog-owner interaction and reunion can increase peripheral
oxytocin levels (Handlin et al., 2011; Rehn et al., 2014).
Similar to Kis et al. (2014), we found that the individual genotype of the OXTR
19131AG polymorphism is associated with human-directed social behavior in
dogs. They also identified a breed effect where German Shepherds carrying the
A-allele scored higher on friendliness while the opposite effect was found in
Border Collies. In our case, golden retrievers with the AA genotype had a
significantly shorter latency to seek physical contact from their owner. Oliva et al.
(2016) did not find any associations between genomic differences and object
choice task performance. However, this could be due to the fact that they studied
a group of mixed breeds while Kis et al. (2014) demonstrated that OXTR gene
polymorphisms could have opposing effects in different breeds. Another reason
could be that they investigated microsatellites further away from the OXTR-gene
than the three previously known polymorphisms.
Considering the opposing effects of oxytocin, OXTR-SNP variants and breed
interactions on dogs’ human-directed social behavior, it is reasonable to assume
that individuals with different OXTR-SNP variants respond differently to oxytocin
administration. We found that golden retrievers carrying the AA genotype of the
19131AG SNP sought more physical contact from their owners upon oxytocin
treatment while GG individuals reacted in the opposite direction and no
differences were found in heterozygotes. In humans, OXTR-gene variants have
been shown to modulate the effect of intranasal oxytocin treatment. Feng et al.
(2015) found that oxytocin increased the brain response to reciprocal behavior
in men with the GG genotype of one polymorphism (rs53576) while the opposite
effect was found in women. Additionally, recent research on oxytocin as a
treatment for autism spectrum disorder found that its efficiency is dependent on
OXTR-gene genotype (Kosaka et al., 2016).
There is increasing evidence of polymorphisms located in non-coding sequences
to be associated with behavioral effects (Banlaki et al., 2015; Persson et al.,
2016). In our case, the associated polymorphism is located in the 3’ untranslated
region immediately after the last exon of the dog OXTR-gene. Therefore, this
variant does not alter the protein coding sequence, but serves merely as a
marker related to any polymorphism in linkage disequilibrium (Schaub et al.,
2012). Since the included markers have been associated with behavior
phenotypes they should be associated with close-by genomic differences
possibly affecting the OXTR-gene.
Although it is highly unlikely that 19131AG in fact is a causative SNP altering
dogs’ human-directed social behavior, we can not exclude a possible involvement
in gene regulation. Non-coding polymorphisms in the 3’ untranslated region can
affect microRNA binding and affect gene expression (Kovacs-Nagy et al., 2013;
Zhao et al., 2013). Additionally, non-coding genetic variation such as intronic
polymorphisms can alter splicing (Lalonde et al., 2011) and have a long-distance
effect on gene regulation (Maurano et al., 2012; Visser et al., 2012). Hence, we
cannot exclude the possibility that the 19131AG SNP has a causal behavioural
effect on dog behaviour. However, it is important to note that this study merely
shows a trait association and the SNP most likely reflects other close-by genomic
differences.
We found that female golden retrievers sought significantly more human eye
contact than males. This is in agreement with previous results showing that
human-directed social behavior in dogs differs between sexes where females
seek more physical contact from humans than males (Persson et al., 2015; Roth
and Jensen, 2015). Also, oxytocin treatment has been shown to have different sex
dependent effects on human directed gazing, increasing looking behavior in
females (Kovacs et al., 2016a; Nagasawa et al., 2015; Oliva et al., 2015). In this
study, males and females did not differ in their response to the oxytocin
treatment. Also, no effects of sex and genotype were shown. However, this could
be due to the fact that there were only four males and four females with the AA-
genotype. To identify such effects one would need to study a larger population or
a population with more evenly divided genotypes.
Our dogs were tested in a repeated measures design, so half of the individuals
received oxytocin treatment at the first testing occasion and saline control
treatment at the second. Somewhat unexpected, we found that dogs receiving
oxytocin at the first testing occasion sought less experimenter physical contact
across both trials. Test order also had an effect independent of treatment where
dogs sought more contact with the experimenter at the second occasion.
Experiences of the experimenter at the first visit may therefore have influenced
their social behavior at the second occasion. This shows that factors such as
treatment order and testing occasion are important to take into consideration
when planning a repeated measures design for investigating effects of oxytocin
on dog social behavior.
Conclusions This is to our knowledge the first study to report different effects of oxytocin
treatment associated with an OXTR polymorphism in dogs. We have shown that
some of the opposing breed specific effects of oxytocin treatment found in other
studies could be a result of OXTR-SNP variation. We have also presented the
genotype frequencies of three previously known SNPs in one novel dog breed,
the golden retriever, and a novel species, the wolf (Canis lupus lupus). By doing
so, we have contributed to an increased knowledge of OXTR-polymorphism
frequencies across dog breeds but also through the domestication process from
wolf to dog.
Acknowledgements We are grateful to all the owners and their dogs participating in this study. A special thanks to SBK Gothenburg for letting us arrange testing around their facilities. This project was funded by the European Research Council (ERC) within the advanced grant ‘GENEWELL’ (322206).
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Figure captions
Oxytocin and a polymorphism in the oxytocin receptor gene
are associated with human-directed social behavior in golden
retriever dogs
Mia E. Persson, Agaia Trottier, Johan Bélteky, Lina S.V. Roth &
Per Jensen*
Figure 1: A schematic figure of the dog OXTR gene. The region pictured
ranges from 9358932 – 9378248 bp starting with a short un-translated region
(UTR) (CanFam 3.1). The SNPs genotyped in this current study are marked with
red lines at 9359329 bp (-212AG), 9378660 bp (rs8679684) and 9378754 bp
(19131AG).
Figure 2: Genotype frequencies of the 19131AG OXTR SNP. Number of dogs
(Count) carrying the AA, AG or GG alleles of the SNP out of A) 26 male and 34
female golden retrievers and B) 21 wolves.
Figure 3: Effects of oxytocin treatment (OT) on experimenter physical
contact in golden retrievers. Comparison of the mean frequency of physical
contact seeking with the experimenter after oxytocin or saline treatment ( p <
0.01, Cohen’s d = 0.47). Error bars show ± 1 SEM.
Figure 4: Effect of 19131AG OXTR genotype on mean latency to seek owner
physical contact. Latency of individuals with the AA-genotype differ
significantly from those with the AG-genotype (Bonferroni adjusted p < 0.01,
Cohen’s d = 1.45) and the GG-genotype (Bonferroni adjusted p < 0.01, Cohen’s d
= 1.43). Asteriskes indicate significant difference from the post hoc test ( p <
0.05). Error bars display ± 1 SEM.
Figure 5: Effects of the interaction between 19131AG OXTR genotype and
oxytocin treatment (OT) on owner physical contact. Shown is mean
frequency of physical contact with the owner and the effects of oxytocin
treatment on individuals carrying the AA-genotype (Bonferroni adjusted p =
0.06, Cohen’s d = 0.95) and the GG-genotype (Bonferroni adjusted p < 0.01,
Cohen’s d = 0.81). No significant difference was found for individuals carrying
the AG-genotype. Asterisks show post hoc significance p < 0.05. Error bars show
± 1 SEM.
Behaviour Akaike Model Data LG10 DistributionDuration experimenter 197 Sex, treatmen yes Normal identityFrequency experimenter 259 Sex, treatmen no Gamma logLatency experimenter 217 Sex, treatmen yes Normal identityDuration experimenter look 132 Sex yes Normal identityFrequency experimenter look 280 Sex no Gamma logLatency experimenter look 206 Sex, treatmen yes Normal identityDuration experimenter physical 50 Treatment yes Normal identityFrequency experimenter physical 109 Treatment yes Normal identityLatency experimenter physical 81 Sex, treatmen yes Normal identityDuration owner 190 Sex yes Normal identityFrequency owner 69 Sex, treatmen yes Gamma logDuration owner look 164 Sex, treatmen yes Gamma logFrequency owner look 268 Sex, treatmen no Gamma logLatency owner look 206 Sex, treatmen yes Normal identityDuration owner physical 89 treatment, 19 yes Normal identityFrequency owner physical 51 Sex, treatmen yes Normal identity
Latency owner physical 6 19131 yes Normal identityDuration Human 162 Sex, treatmen yes Normal identityFrequency Human 48 Sex, treatmen yes Normal identityDuration Look 167 Sex, treatmen yes Normal identityFrequency Look 114 Sex, treatmen yes Normal identityDuration Physical 139 Sex, treatmen yes Normal identityFrequency Physical 136 19131xtreatmyes Normal identity
Suggestive factor Significant factor F p df1 df2 Mean1 (Female/OT/AA)
Sex 5.133 0.025 1 118 8.13Sex 7.851 0.006 1 118 10.12
Treatment 3.039 0.084 1 118 0.89Treatment 6.533 0.012 1 118 1.7
Sex 4.3 0.04 1 118 18.5
Treatment x 19131 2.501 0.087 2 114Treatment x 19131 5.208 0.007 2 113
Sex 3.596 0.06 1 11319131 7.165 0.001 2 117 129.56
Treatment x 19131 2.994 0.054 2 114
SEM Mean2 (Male/PBS/AG) SEM Mean3 (GG) SEM
1.58 3.89 0.711.09 6.58 0.72
0.23 1.48 0.360.4 3.3 0.88
2.81 32.31 5.49
16.58 160.56 5.78 156.8 5.9
Behaviour Significant factor F p df1 df2Duration experimenter Occasion 9.909 0.002 1 117Frequency experimenter Occasion 6.29 0.014 1 117Duration experimenter look Occasion 19.055 0 1 117Frequency experimenter look Occasion 24.697 0 1 117Frequency owner look Occasion 8.419 0.004 1 117Duration experimenter physical First treatment 4.867 0.029 1 117
Mean1(first occ/OT first) SEM Mean2 (2nd occ/PBS first) SEM13 1.91 19.86 2.41
5.67 0.57 7.1 0.683.52 0.57 9.06 1.785.93 0.6 11.23 1.2
8.6 0.95 11.6 1.110.7 0.23 1.7 0.37